1. Technical Field
The present invention relates to electrosurgical generators and, more particularly, to electrosurgical generators which are microprocessor-controlled to permit use by more than one surgeon from a single unit and to provide accurate adjustable control of the cutting signal power level.
2. Discussion of the Prior Art
Electrosurgical generators of the type with which the present invention is concerned are described and illustrated in the following U.S. Pat. Nos.: 4,038,984 (Sittner); 4,188,927 (Harris); 4,318,409 (Oosten); 4,378,801 (Oosten); 4,429,694 (McGreevy); 4,438,766 (Bowers); and 4,473,075 (Rexroth). To the extent that such patents provide a general background and understanding of the electrosurgical generator field and technology, the disclosures in those patents are expressly incorporated herein, in the entireties, by this reference.
Electrosurgical generators are capable of operating in four primary surgical modes, namely: dessication; fulguration; cutting; and cutting with hemostasis. Dessication and fulguration are considered parts of a coagulation mode. The level and waveform of the r-f power of voltage applied to the surgical site differs for the various modes.
The signal for performing electrosurgical operations is typically generated by a radio-frequency (r-f) generator connected to a power amplifier. The output signal from the power amplifier is delivered to the tissue mass by means of two electrodes. Monopolar surgical operations are performed by means of an active electrode which introduces the r-f current into the tissue mass. A dispersive patient return pad constitutes the second electrode. The active electrode typically has a small cross-section to concentrate the power and to limit the surgical effect to a small controlled area. The return path from the tissue mass to the generator is provided by the dispersive pad which has a large area to prevent electrosurgical effects from taking place at the current return location. Alternatively, a pair of active electrodes may be employed in a bipolar mode in which the electrosurgical effects are confined to the tissue located between the two electrodes.
In the cutting mode, the cutting signal is a high frequency signal which serves to cut through tissue when the signal is applied to the patient. The electrode is used to apply the electrical energy to defined and concentrated points at the surgical site. Cutting is accomplished by the concentrated application of r-f energy which effectively destroys body cells directly beneath the electrosurgical electrodes. Coagulation signals are intended to produce coagulation by shrinking vessel walls. Typically, such coagulation signals are pulses of energy having a damped sinusoidal waveform. Coagulation signals may be viewed as causing cell dehydration to produce coagulation rather than destroying cells in the fashion of cutting signals. Blended signals are formed by combining the cutting and coagulation signals, and are useful for accomplishing cutting and coagulation simultaneously. Alternating periods of each signal may be employed to form the blended signal.
It is desirable to provide electrosurgical generators with power adjustments so that surgeons can adjust the power level as necessary in each of the operating modes. Power adjustability is available in prior art electrosurgical generators; however, the adjustment is neither sufficiently accurate nor sufficiently precise for many delicate surgical procedures.
Moreover, prior art electrosurgical generators cannot be employed by two or more surgeons, using respective surgical pencils, with independent mode and power control for each pencil.
Another problem with prior electrosurgical generators concerns the need for removing the dispersive patient return pad when changing from monopolar to bipolar operation, and the replacing of the pad when returning to monopolar operation. If the pad is not removed for bipolar operation, the cutting signal is at least partially diverted from its path between the two bipolar electrodes to unwanted paths from either or both electrodes to the pad.